We fabricated nanocomposites by dispersing uniform-sized silica nanospheres (SNSs, 49-282 nm, 0-30 wt%) into polypropylene (PP) and two types of functionalized PP to clarify the effects of matrix-filler interfacial adhesion forces on the mechanical properties in PP-based nanocomposites. Since there is good affinity between silica surfaces and hydroxyl group in PP, poly(5-hexen-1-ol-co-propylene) with 1.3 and 6.4 mol% of hydroxyl groups were employed as functionalized PP (PPOH). Tensile tests revealed that some mechanical properties of the composites with PPOH were higher than those with PP. In particular, composites with PPOH maintained high ductility, whereas the ductility of composites with PP were significantly reduced by dispersing SNSs. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) studies indicated the formation of hydrogen bonds between PPOH and the silica surface, which are attributed to the high ductility. (C) 2016 Elsevier Ltd. All rights reserved.